The present invention relates to an exemplary device and an exemplary method for stabilizing a combination of a tractor and at least one semitrailer or trailer. In this connection, the tractor vehicle can be a passenger car or a truck, and a trailer can be a truck trailer or even a trailer for a passenger car, such as for example, a recreational trailer.
In German Published Patent Application No. 25 47 487 is discussed a device for stabilizing a vehicle which includes at least one guide part and one propulsion part. In that case, the propulsion part is connected to the guide part by a link. The device has a sensor for sensing the bending angle occurring between the guide part and the propulsion part. A sensor is also provided for measuring the steering angle. The device includes an evaluation circuit to which the signals from the two sensors are transmitted, and which generates an output signal when the bending angle exceeds specified angle magnitudes, which are dependent on the steering angle. The specified angle magnitudes correspond to the bending angle, which is determined as a function of the steering angle, and which is permissible in any particular driving situation. Furthermore, the device is provided with a unit for automatically controlling braking pressure to at least one axle of the propulsion part, the unit being activated by the output signal of the evaluation circuit.
An object of an exemplary embodiment of the present invention is to provide an improved device and method, respectively, for stabilizing a combination of a tractor and at least one semitrailer or trailer.
In an exemplary embodiment, a combination of a tractor vehicle and at least one semitrailer or trailer may be stabilized by having the brakes of the at least one semitrailer or trailer be set automatically, as a function of the yaw rate of the tractor and the setpoint yaw rate of the tractor. Alternatively, the brakes of the at least one semitrailer or trailer are set automatically, depending on the yaw rate of the tractor vehicle, the speed of the combination and the steering angle, the setpoint yaw rate being advantageously ascertained from the speed of the combination and the steering angle. The calculation of the setpoint yaw rate of the tractor vehicle from the speed of the combination and the steering angle is discussed, for example, in the article, FDRxe2x80x94Die Fahrdynamikreglung von Bosch (FDRxe2x80x94The Vehicle Dynamics Control of Bosch), by A. van Zanten, R. Erhardt and G. Pfaff, ATZ Automobiltechnische Zeitschrift, (Journal of Automobile Technology) 96 (1994), 11, pages 674 to 689, or the article, Vehicle Dynamics Controller for Commercial Vehicles, by F. Hecker, S. Hummel, O. Jundt, K.-D. Leimbach, I. Faye, and H. Schramm, SAE 973284, 1997, pages 59 to 66. Measuring the bending angle, as may be required, for example, in the design approach of German Published Patent Application No. 25 47 487, is not believed to be necessary here.
According to an exemplary embodiment of the present invention, a combination of a tractor vehicle and at least one semitrailer or trailer may be stabilized by setting the brakes of the at least one semitrailer or trailer, in particular automatically, so that the semitrailer or trailer is braked more strongly than the tractor vehicle when the yaw rate of the tractor vehicle is greater, in particular by a tolerance value, than the setpoint value of the yaw rate of the tractor vehicle. That means that the semitrailer or trailer is braked when the tractor vehicle oversteers. Measuring the bending angle, as may be required, for example, in the design approach of German Published Patent Application No. 25 47 487, is not believed to be necessary here. The subject matter of the exemplary embodiment of the present inventions may be applied to vehicle combinations. This can be a combination including a tractor vehicle and a semitrailer or trailer, or it can be a combination including a passenger car and, for example, a recreational vehicle.
Such a setting of the brakes of the at least one semitrailer or trailer, in which the semitrailer or trailer is braked more strongly than the tractor vehicle when the yaw rate of the tractor vehicle is greater, particularly by a tolerance value, than the setpoint value of the yaw rate of the tractor vehicle, is affected advantageously in that the semitrailer or trailer is braked more strongly than the tractor vehicle when the following holds:
|xcfx89*xe2x88x92xcfx89xe2x89xa7c1,
and
sign(xcex94xcfx89)xe2x89xa0sign(xcfx89)
xcex94xcfx89=xcfx89*xe2x88x92xcfx89,
and
where xcfx89 is the yaw rate, xcfx89* is the setpoint yaw rate and c1 is the tolerance value.
In an exemplary embodiment of the present invention, the semitrailer or trailer is braked more strongly than the tractor vehicle when the following holds:       sign    ⁡          (                                    ⅆ            Δ                    ⁢                      xe2x80x83                    ⁢          ω                          ⅆ          t                    )        =            sign      ⁡              (                  Δ          ⁢                      xe2x80x83                    ⁢          ω                )              .  
In a another exemplary embodiment of the present invention, the semitrailer or trailer is braked more strongly than the tractor vehicle when the following holds:             "LeftBracketingBar"                        ⅆ          Δω                          ⅆ          t                    "RightBracketingBar"        ≥    c2    ,
where c2 is an additional tolerance value.
Both tolerance value c1 and tolerance value c2 can, for instance, be determined in two different ways. In the first way, tolerance value cl and tolerance value c2 can each be a single value. This single value is determined by driving experiments and theoretical considerations in the preliminary stage, i.e., within the framework of developing the application. In this case, it is a fixedly specified and nonchangeable tolerance value, which cannot be adapted to the driving situation during vehicle travel.
In the second way, tolerance value c1 and tolerance value c2 can each be stored in the form of a characteristic curve or in the form of a family of characteristics (multidimensional characteristic curve). The characteristic curve, or the family of characteristics, as the case may be, is also determined by driving experiments and theoretical considerations in the preliminary stage, i.e., within the framework of developing the application. For this purpose, the behavior of the vehicle in different driving situations is evaluated with regard to values, appearing in these driving situations, for the terms:       "LeftBracketingBar"                  ω        *            -      ω        "RightBracketingBar"    ⁢      xe2x80x83    ⁢  or  ⁢      xe2x80x83    ⁢            "LeftBracketingBar"                                    ⅆ            Δ                    ⁢                      xe2x80x83                    ⁢          ω                          ⅆ          t                    "RightBracketingBar"        .  
That means that at different vehicular speeds or at different steering angles or at different coefficients of friction of the road surface, respectively, those values of these terms are calculated, which characterize or correspond to an incipient instability of the vehicle combination, or at which the vehicle combination begins to behave unstably. These values are then stored in the form of a characteristic curve or family of characteristics. The quantities indicated above, namely, vehicular speed, steering angle, and coefficient of friction of the road surface, respectively, are then constantly determined during the operation of the vehicle. These quantities are used as input values for the characteristic curve or family of characteristics. The tolerance value c1 or c2 corresponding to each driving situation is then ascertained as a function of these input variables. Consequently, using this procedure, both tolerance values c1 and c2 are permanently adapted to the prevailing vehicle situation. In this manner, therefore, it is possible to set different tolerance values, for example, for a highway trip (longer time, greater vehicle speed and, with that, no great steering angle changes) than for driving in city traffic (lower vehicle speed, with greater steering angle changes at the same time).
In a another exemplary embodiment of the present invention, the semitrailer or trailer is braked more strongly than the tractor vehicle vehicle when the following holds:
|xcfx89*xe2x88x92xcfx89|xe2x89xa7c1,
sign(xcex94xcfx89)xe2x89xa0sign(xcfx89),
                    sign        ⁡                  (                                                                      ⅆ                  Δ                                ⁢                                  xe2x80x83                                ⁢                ω                                            ⅆ                t                                      ⁢                          xe2x80x83                                )                    =              sign        ⁡                  (                      Δ            ⁢                          xe2x80x83                        ⁢            ω                    )                      ,    and                      "LeftBracketingBar"                                            ⅆ              Δ                        ⁢                          xe2x80x83                        ⁢            ω                                ⅆ            t                          "RightBracketingBar"            ⁢              xe2x80x83            ≥              xe2x80x83            ⁢      c2        ,  
where
xcex94xcfx89=xcfx89*xe2x88x92xcfx89.
In another exemplary embodiment of the present invention, the at least one semitrailer or trailer is essentially braked equally on both sides.
In another exemplary embodiment of the present invention, the setting of the brakes of the at least one semitrailer or trailer as a function of the yaw rate of the tractor vehicle vehicle and the setpoint yaw rate of the tractor vehicle , or as a function of the yaw rate of the tractor vehicle, the speed of the combination and the steering angle is, in particular, immediately discontinued when there has been a change in the algebraic sign of the yaw acceleration. Alternatively, a test is made as to whether the magnitude of the yaw acceleration lies in a small range around zero. This range is defined by a small range around zero, i.e. the range corresponds to the interval from xe2x88x92GB 1 to +GB 1. Consequently, the braking of the semitrailer or trailer is discontinued at the point when, for positive yaw accelerations, the yaw acceleration is less than +GB 1, or when, for negative yaw accelerations, it is greater than xe2x88x92GB1.
Stronger braking of the semitrailer or trailer than of the tractor vehicle, within the context of the exemplary embodiment of the present invention, refers to the semitrailer or trailer being braked, but not the tractor vehicle. If, for certain reasons, for instance due to operation of the brake by the tractor vehicle driver, a braking signal also reaches the brakes of the tractor vehicle, according to the exemplary embodiments of the present invention, the brakes of the semitrailer decelerate the latter more strongly than the tractor vehicle, i.e. the semitrailer or the trailer is braked more strongly than the tractor vehicle.